1. In the Calvin cycle, the enzyme that catalyzes the regeneration of ribulose-1,5-bisphosphate (RuBP) from ribulose-5-phosphate is:

  • A. Rubisco
  • B. Phosphoribulokinase
  • C. Aldolase
  • D. Transketolase

Answer: B. Phosphoribulokinase

Explanation: Phosphoribulokinase catalyzes the ATP-dependent phosphorylation of ribulose-5-phosphate to regenerate RuBP.

2. Which soil colloid contributes the greatest proportion of pH-dependent negative charge?

  • A. Kaolinite
  • B. Humus
  • C. Quartz
  • D. Hematite

Answer: B. Humus

Explanation: Humus has numerous carboxyl and phenolic groups that dissociate with increasing pH, producing a very high pH-dependent CEC.

3. Double fertilization in angiosperms results in the formation of:

  • A. Embryo and perisperm
  • B. Embryo and endosperm
  • C. Cotyledons and seed coat
  • D. Ovule and nucellus

Answer: B. Embryo and endosperm

Explanation: One sperm fuses with the egg to form the embryo, while the other fuses with the polar nuclei to produce the triploid endosperm.

4. Which enzyme initiates biological nitrogen fixation by reducing atmospheric nitrogen to ammonia?

  • A. Nitrogenase
  • B. Nitrate reductase
  • C. Nitrite reductase
  • D. Glutamine synthetase

Answer: A. Nitrogenase

Explanation: Nitrogenase is the enzyme complex responsible for converting atmospheric nitrogen (N₂) into ammonia under biological conditions.

5. Which of the following is a quantitative trait generally controlled by many genes?

  • A. Flower colour
  • B. Seed shape
  • C. Grain yield
  • D. Cotyledon colour

Answer: C. Grain yield

Explanation: Grain yield is a complex quantitative trait influenced by multiple genes and environmental factors.

6. Which nutrient deficiency is commonly associated with the appearance of "whiptail" in cauliflower?

  • A. Zinc
  • B. Boron
  • C. Molybdenum
  • D. Iron

Answer: C. Molybdenum

Explanation: Molybdenum deficiency causes whiptail in cauliflower due to improper leaf blade development.

7. The chromosome number of bread wheat (Triticum aestivum) is:

  • A. 2n = 14
  • B. 2n = 28
  • C. 2n = 42
  • D. 2n = 56

Answer: C. 2n = 42

Explanation: Bread wheat is a hexaploid species (AABBDD genomes) with 2n = 42 chromosomes.

8. Which insect pest is known as the "dead heart" pest of rice during the vegetative stage?

  • A. Rice gall midge
  • B. Brown planthopper
  • C. Yellow stem borer
  • D. Rice hispa

Answer: C. Yellow stem borer

Explanation: Yellow stem borer larvae bore into rice stems, producing dead hearts during the vegetative stage and white ears at maturity.

9. The Kjeldahl method is primarily used for estimating:

  • A. Available phosphorus
  • B. Organic carbon
  • C. Total nitrogen
  • D. Potassium

Answer: C. Total nitrogen

Explanation: The Kjeldahl method determines total organic nitrogen and ammonium nitrogen in plant and soil samples.

10. Which law states that crop yield is limited by the essential nutrient available in the least amount relative to crop requirement?

  • A. Mitscherlich's Law
  • B. Liebig's Law of the Minimum
  • C. Shelford's Law of Tolerance
  • D. Blackman's Law

Answer: B. Liebig's Law of the Minimum

Explanation: Liebig's Law states that plant growth is controlled by the nutrient in shortest supply relative to plant demand.